This invention is in the field of glass fiber reinforced polyethylene terephthalate molding compounds.
Polyethylene terephthalate molding compounds which are reinforced with glass fibers, asbestos fibers, or other fibrous mineral material are known, as are polyethylene terephthalate blends which are able to crystallize relatively rapidly (as desired) after being injection molded into the typical water cooled molds employed in the injection molding industry (which attain surface mold temperature ranging from about 85.degree. to 100.degree. C.). Oil cooled molds, which have higher mold surface temperatures, may, of course, be used if desired.
Objects molded of polyethylene terephthalate compounds filled with glass fibers have varying degrees of warpage due to differential shrinkage once the objects are removed from the molds.
It is difficult to get fiber reinforced polyethylene terephthalate molding blends with a combination of acceptably high, from a commercial viewpoint, thermal and mechanical properties which also have low warpage. Thus, even when a particular polyethylene terephthalate molding compound displays both good surface finish and crystallization characteristics and, after injection molding, some good strength characteristics, it may not be suitable for use in many molding resin blend applications, because of excessive warpage. For example, for use in so called engineering resin applications, a glass fiber reinforced polyethylene terephthalate molding compound needs to have good spiral flow, rapid crystallization, high heat distortion temperature, and an ability to produce a molded part which has a smooth, glossy surface and minimal warpage after the part is removed from a mold.
A fiber reinforced polyethylene terephthalate resin compound intended for engineering resin applications and which accordingly has a commercially acceptable combination of desirable physical and chemical properties should also be capable of having a flame retardant material added thereto in an amount effective for achieving flame retardancy without a significant or commercially unacceptable loss of properties.
There is a need in the art for reinforced polyethylene terephthalate molding compounds with low warpage and high flow characteristics under molding conditions, which also have engineering resin performance characteristics. Also, there is a need in the art for compounds of this type which display high flow rates under molding conditions without water addition and without lubricant addition. In addition, it would be desirable for such blends to have the capacity to be flame retarded to an acceptable extent by the admixture therewith of flame retardant(s) without excessive loss of performance characteristics.